The present invention relates to a circuit protection apparatus that prevents a circuit from being closed when attempting to charge a battery with incorrect polarity connections or attempting to charge a battery from a potentially hazardous higher voltage power source. The apparatus is particularly useful as a motor vehicle jump start protection system and as a short circuit protection system.
When a battery of a first motor vehicle is flat (no power), it is known to connect a battery from a second vehicle source across the flat battery in order to start the engine of the first vehicle. Such a technique is commonly referred to as jump starting. It is also known that a flat battery may be recharged by connecting a power source such as a battery charger across the flat battery.
When the battery of a motor vehicle is difficult to access or is not located in the engine compartment, but elsewhere in the vehicle, it has become common practice to provide jump start terminals in the engine compartment which can be connected to either a battery of a second vehicle or a battery charger should the battery of the first vehicle go flat. If the second battery or the battery charger is incorrectly connected (that is, the wrong polarity) to the jump start terminals, electrical components in the first vehicle (especially diodes associated with the generator of the first vehicle) may be damaged. Other conditions which cause the jump start terminal to short circuit to ground can also cause damage.
Weber, U.S. Pat. No. 5,230,637, describes what can happen when sparking or a damaged battery are present when jump starting a vehicle.
As the need for energy in motor vehicles increases with the addition of more electrically powered components and systems, vehicle manufacturers are contemplating higher voltage electrical architectures. The introduction of higher voltage systems increases the probability that someone will try to jump start or recharge a conventional 12 volt battery from a source that has a higher voltage. This situation can damage the battery or electrical components in the vehicle. Use of higher voltages also increases other risks resulting from sparking.
The prior art includes inventions that address the problem of reverse polarity connections when jump starting a battery. Weber ""637 provides for jumper cables with reverse polarity protection. Another example of a jump start protection system is described in Alksnat, et al., U.S. Pat. No. 6,211,577. Alksnat ""577 utilizes a jump start circuit, a switch, a logic circuit, and a timer circuit. The ""577 patent monitors polarity differences across the jump start terminals and closes the jump start circuit switch if polarities match. A timer circuit is used to open the switch after a predetermined period of time. A manual push button is provided to enable the operator to manually close the jump start circuit switch when a second vehicle is used for jump starting.
In the prior art, in order to provide jump start or reverse polarity connection protection it is necessary that either special jump start cables are used or additional operator actions are performed over and above the traditional jump start method.
The present invention overcomes the problems noted above and satisfies the need in this field for a device that can provide protection during jump starting without the need for additional operator actions or special jump start cables.
A preferred embodiment of the present invention operates by monitoring voltages at a jump start post and the positive terminal of a DC power source such as a battery. When a jump start is correctly initiated on a flat battery of a first vehicle using an appropriate battery charger or good battery from a second vehicle and correct polarity connections, a microprocessor in the jump start circuit on the first vehicle determines that the values of the two voltages fall within an allowable range of values. The microprocessor then commands that a normally open switch positioned in a circuit between the jump start post and the positive terminal of the battery be closed.
The microprocessor commands the switch to open based on one or more of many possible conditions, such as receiving input from another vehicle module, detection of a condition indicating the jump start connection has been disengaged, detection of a condition precedent to jump start connection disengagement, detection of reverse polarity connections, detection of a short circuit condition or other possible conditions.
When a jump start is incorrectly attempted (e.g., due to reverse polarity connections, connection to a higher voltage power source or inadvertent connection of the positive and negative terminals of the same battery (short circuit)), the switch remains open because the measured voltages fall outside an allowable range of values. Similarly, if a short circuit or other condition causes one or more functions to fall outside an allowable range of values during the course of a jump start the microprocessor commands the switch to open.
In accordance with the present invention a jump start circuit is provided for electrical connection between a positive battery terminal and a jump start post. The jump start circuit includes a switch configured to be coupled between the positive battery terminal and the jump start post. In a preferred embodiment, the switch is biased to a normally open position. The switch has a closed state and an open state, where the switch operates to connect the positive battery terminal to the jump start post when in the closed state and the switch also operates to disconnect the positive battery terminal from the jump start post when in an open state. The jump start circuit further includes a resistor coupled between the positive battery terminal and the jump start post in parallel with the switch. In addition, the jump start circuit also includes a microprocessor that measures voltage at the positive battery terminal and the jump start post, processes the voltage measurements, and commands the switch to close when predetermined conditions are satisfied. The microprocessor commands the switch to open when other predetermined conditions are satisfied.
An advantage of the present invention is that it provides protection against incorrect polarity connection during vehicle jump starting and battery charging.
It is yet another advantage of the present invention to provide protection against jump starting with an inappropriate higher voltage battery.
Yet still another advantage of the present invention is that it enables jump starting with no requirements for additional operator actions over and above the traditional jump start method.
Another advantage of the present invention is that it provides protection if the battery positive potential is short circuited to ground during vehicle jump starting and battery charging.
Still another advantage of the present invention is that it provides short circuit protection for a circuit that connects a power source to a load by preventing a switch from closing the circuit when a short circuit condition exists in the circuit between the switch and the load.
A feature of the present invention is that it can be utilized to provide a cold jump start connection and disconnection, thereby eliminating sparking while connecting and disconnecting jumper cables.